The invention relates generally to digital image scaling whereby raster image of one particular spatial resolution is converted to a like image having a different spatial resolution. More particularly, the invention relates to a method and apparatus for reducing or enlarging gray-scale images by a rational scale factor.
Image scaling is often employed when an image is created, processed or stored on one system or device or subsequently transferred for use, display or output to another device. Image enlarging is especially useful where raster images which require large amounts of computer memory are stored in compressed form and then enlarged for display or hard copy output.
There is therefore seen a need for a fast and computationally efficient method for reducing or enlarging gray-scale images by a variable amount. It is also desirable that the method be useful on images having any number of gray levels and that the method produce output images of as good or better quality than those produced using other known scaling techniques. Finally, such methods should be easily and conveniently implementable in hardware.